GCSE Physics (AQA)

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Measuring Speed of Sound - Echoes

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Waves Waves in air, fluids and solids

Measuring Speed of Sound - Echoes

4:25 Wave Speed
Spec 4.6.1.2
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  • Loud sound waves can reflect off large surfaces like buildings, cliffs, mountains, and cave walls to create echoes.
  • An echo is formed when a sound wave is projected towards a surface, reflects off it without being absorbed, and travels back with unchanged speed, wavelength, and frequency, although its amplitude might decrease.
  • If the reflected sound wave reaches the listener, they hear the original sound as an echo.
  • Understanding echoes is important for exams, where students might need to recall what a reflected sound wave is known as or describe methods to measure the speed of sound using echoes.
  • A method to measure the speed of sound using echoes involves several steps:
  • 1. Measure the distance to the reflecting surface (e.g., a building) ensuring it's not too far to prevent hearing the echo or too close to receive the echo too quickly.
  • 2. Start a stopwatch as you project a sound towards the building using a loud noise like yelling or an air horn.
  • 3. Stop the stopwatch as soon as the echo is heard.
  • 4. Halve the recorded time to determine the time it took for the sound to reach the building, considering the sound travels the distance twice (to the building and back).
  • 5. Calculate the speed of sound by dividing the distance by the time it took for the sound to travel to the building.
  • The speed of sound can be calculated as approximately 330 meters per second if it takes about 0.3 seconds to travel 100 meters.
  • In exams, students might need to perform similar calculations or suggest methods to improve the accuracy of such measurements, like averaging the times of multiple echoes.

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